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Questions 1

(a) Topic -8.1 Rate of reaction

(b)Topic – 8.1 Rate of reaction

(c)Topic -8.1 Rate of reaction

Fluorine reacts with chlorine dioxide, ClO₂, as shown.
F₂(g) + 2ClO₂(g) → 2FClO₂(g)
The rate of the reaction is first order with respect to the concentration of F₂ and first order with respect to the concentration of ClO₂. No catalyst is involved.
(a) (i) Suggest a two-step mechanism for this reaction.
(ii) Identify the rate-determining step in this mechanism. Explain your answer.
(b) When the rate of the reaction is measured in moldm⁻³ s⁻¹, the numerical value of the rate constant, k, is 1.22 under certain conditions.
(i) Complete the rate equation for this reaction, stating the overall order of the reaction.

(ii) Use your rate equation in (i) to calculate the rate of the reaction when the concentrations of F₂ and ClO₂ are both 2.00 × 10⁻³ mol/dm³.

(c) Under different conditions, and in the presence of a large excess of ClO₂, the rate equation is as shown.
rate = \(k_1[F_2]\)
The half-life, \(t_\frac{1}{2}\), of the concentration of \(F_2\) is 4.00s under these conditions.
(i) Calculate the numerical value of \(k_1\), giving its units. Give your answer to three significant figures.
\(k_1\) = ………………………… units …………………………
(ii) An experiment is performed under these conditions in which the starting concentration of F₂ is 0.00200 mol/dm³.  Draw a graph on the grid in Fig. 1.1 to show how the concentration of \(F_2\) changes over the first 12 s of the reaction.

(iii) Use your graph in Fig. 1.1 to find the rate of the reaction when the concentration of \(F_2\) is 0.00100 mol/dm³. Show your working on the graph.

▶️Answer/Explanation

Ans:

(a)(i) M1:F2 + ClO₂ → FClO₂ + F [1]
M2:ClO₂ + F → FClO₂ [1]
OR
M1: \(F_2 + ClO_2 → F_2ClO_2\)
M2: \(F_2ClO_2 + ClO_2 → 2FClO_2\)
two balanced equations MUST add to give the overall equation

(ii) first step AND
has one mole / molecule of F₂ and ClO₂ [1]
OR same moles of reactants as orders in rate equation

(b)(i) rate = \(k [F_2][ClO_2]\) /  rate = \(1.22 [F_2][ClO_2]\)
AND second / 2 BOTH [1]

(ii) rate = \(1.22 \times 2 \times 10^{-3} \times 2 \times 10^{-3} = 4.88 \times 10^{-6}\)[1]
min 2sfecf 1(b)(i)

(c)(i) \(k_1 = (0.693 / 4) = 0.173\) OR \(1.73 \times 10^{-1}[1]\)
MUST BE 3SF
\(s^{–1}[1]\)

(ii) at 4 s = 0.001
at 8 s = 0.0005
at 12 s = 0.00025
smooth curve
ALL correct [1]

(iii) tangent drawn at \(0.00100 mol dm^{–3}\)
AND
gradient dependent on their rate = Y / X in the range = \(1.5–2.0 \times 10^{–4}[1]\)
IGNORE sign

Questions 2

(a) Topic -25.1 Acids and bases

(b)Topic – 25.1 Acids and bases

(c)Topic -25.1 Acids and bases

(d)Topic -25.1 Acids and bases

(a) Define \(K_w\) mathematically by completing the expression.

(b) Two solutions, V and W, are described.
• V is HCl(aq).
• W is NaOH(aq).
• The concentration of HCl in V is the same as the concentration of NaOH in W.
• The pH values of V and W differ by exactly 11.00 at 298K.
(i) Calculate the concentration of HCl in V

(ii) Equal volumes of the two solutions V and W are mixed, giving solution X. Name solution X and state its pH.

(iii) A 1 cm³ sample of 1.0 mol/dm³ HNO₃ is added to 100 cm³ of solution X, forming mixture Y. A 1 cm³ sample of 1.0 mol/dm³ KOH is added to 100 cm³ of solution X, forming mixture Z. Estimate the pH of mixtures Y and Z. No calculations are required.

(c) (i) CH₃CH₂COOH, CH₃CCl₂COOH, and H₂SO₄ are all acidic. Suggest the trend in the relative acid strength of these three compounds. Explain your answer

(ii) When concentrated H₂SO₄ is added to water a series of acid-base reactions occurs. There are three conjugate acid-base pairs that can be identified during this series of reactions. Write the formulae of these three conjugate acid-base pairs.
conjugate acid 1 ………………………………….. conjugate base 1 …………………………………..
conjugate acid 2 ………………………………….. conjugate base 2 …………………………………..
conjugate acid 3 ………………………………….. conjugate base 3 …………………………………..
(d) The partition coefficient, \(K_{pc}\), of a substance, Q, between hexane and water is 7.84 at 298K. Q is more soluble in hexane than it is in water.
(i) Define partition coefficient, \(K_{pc}\).

(ii) 5.00g of Q is shaken with a mixture of 100.0 cm³ of water and 100.0 cm³ of hexane at 298K and left until there is no further change in concentrations. Calculate the mass of Q dissolved in the water.

(iii) A sample of Q is shaken with a different mixture of water and hexane and left until there is no further change in concentrations. It is found that the mass of Q dissolved in each solvent is the same. Use the \(K_{pc}\) value to suggest possible values for the volume of water used and the volume of hexane used.

(iv) Q is more soluble in hexane than it is in water. It is suggested that Q is one of KCl, CH₃(CH₂)₄OH, or HCOOH. Identify Q. Explain your answer

▶️Answer/Explanation

Ans:

(a) (\(K_w\) =)[H⁺][\(OH^–\)] OR (Kw =)[H₃O⁺][\(OH^–\)] [1]

(b)(i) M1: pH values 1.5 AND 12.5 [1]
M2: conc of HCl = 10–1.5 = 0.0316 ecf [1]
min 2sf

(ii) sodium chloride / NaCl AND 7 [1]

(iii) (mixture Y) 1 to 3 AND (mixture Z) 11 to 13 [1]

(c)(i) H₂SO₄ > CH₃CCl₂COOH > CH₃CH₂COOH [1] u / c
explanation
• H₂SO₄ is fully dissociated / strong acid
• CH₃CH₂COOH / CH₃CCl₂COOH are partly dissociated / weak acids
• Cl / chlorine is electron-withdrawing / electronegative
• alkyl group (in CH₃CH₂COOH) is electron donating
• stabilises / destabilises anion OR weakens / strengthens O-H bond (linked correctly)
• correct reference to release of / donation of / form \(H^+\) / proton
any two [1] any four [2]

(ii) • H₃O⁺ and H₂O
• H₂SO₄ and HSO₄⁻
• HSO₄⁻ and SO₄²⁻
any one correct pair [1]
all three correct pairs [2]

(d)(i) (the) ratio of the concentrations (of a solute between)
two solvents / two liquids (at) equilibrium [1]

(ii) mass = 5-x / x = 7.84 OR mass = x / 5-x = 7.84
mass = 0.5656 g mass = 4.43 g
[1] min 2sf

(iii) Any numbers in which volume of water is 7.84 times volume of hexane e.g. 78.4 cm³ water 10 cm³ hexane [1] u / c
e.g mass = 0.566 g 177.4 cm³ water 22.6 cm³ hexane
ALLOW reverse ratio volume of hexane is 7.84 times volume of water when consistent with d(ii)

(iv) Q is CH₃(CH₂)₄OH.
AND it is least polar
 / contains a large non-polar hydrocarbon chain
 / stronger id-id forces with hexane in Q OWTTE
[1]

 

 

Questions 3

(a) Topic -23.3 Entropy change, ΔS

(b)Topic – 23.3 Entropy change, ΔS

(c)Topic -23.3 Entropy change, ΔS

(d)Topic -23.3 Entropy change, ΔS

(e)Topic -24.1 Electrolysis

(f)Topic -24.1 Electrolysis

(g)Topic -5.1 Enthalpy change, ΔH

Hydrogen peroxide is a liquid at 298K. It is moderately stable under room conditions but will decompose quickly if a catalyst is added.
reaction 1 \(2H_2O_2(l) \to 2H_2O (l) + O_2 (g)\)
(a) (i) Define entropy.
(ii) Predict the sign of the standard entropy change of reaction 1. Explain your answer.
(b) Some bond energy data are shown in Table 3.1.

Use the data in Table 3.1 to show that the enthalpy change of the following reaction is \(–196 kJ mol^{–1}\).
2H₂O₂(g) \(\to\)  2H₂O(g) + O₂(g)

(c) Some standard entropies, \(S^o\), are shown in Table 3.2.

The enthalpy change and Gibbs free energy change for the following reaction are shown.
2H₂O₂(l) 2H₂O(l) + O₂(g)  \(ΔH^o\) = –196 kJ mol⁻¹
\(ΔG^o = –238kJmol^{–1}\)
Use the data given to calculate the standard entropy of oxygen, \(S^o\) , O₂(g).

(d) The decomposition of H₂O₂(aq) is catalysed by aqueous iron(III) chloride and by silver metal. Identify which of these two catalysts is acting as a homogeneous catalyst. Explain your answer.

(e) The E o values for two electrode reactions are given.
\(H_2O_2 + 2H^+ + 2e^− \rightleftharpoons  2H_2O\)  \(E^o = +1.77V\)
\(Cr^{3+} + e^− \rightleftharpoons Cr^{2+}\)  \(E ^o = −0.41V\)
(i) An electrochemical cell is constructed with the following half-cells (electrodes):
• an acidified solution of H₂O₂, a platinum wire
• Cr²⁺ mixed with Cr³⁺, a platinum wire.
Identify the positive half-cell and calculate the standard cell potential, \(E^o_{cell}\).
(ii) Calculate the value of ΔG o for the cell reaction that occurs, per mole of H₂O₂.

(f) The \(E^ o\) values for two electrode reactions are given.
\(H_2O_2 + 2H^+ + 2e^− \rightleftharpoons  2H_2O\)  \(E^o = +1.77V\)
\(Co^{3+} + e^– \rightleftharpoons Co^{2+}\)  \(E ^o = +1.82V\)
An electrochemical cell is constructed with the following half-cells.
half-cell 1 an acidified solution of H₂O₂ under standard conditions, a platinum wire
half-cell 2 a solution containing 0.020 moldm⁻³ Co³⁺ and 2.0 moldm⁻³ Co²⁺, a platinum wire
(i) Use the Nernst equation to calculate the value of E, the electrode potential of half-cell 2 under these conditions.

(ii) Write an equation for the cell reaction that occurs in this cell under these condition.

(g) (i) Define enthalpy change of hydration, \(\Delta H_{hyd}\).
(ii) Aluminium fluoride, AlF₃, is an ionic solid.
Complete and label the energy cycle to show the relationship between:
● the enthalpy change of solution of AlF₃, \(\Delta H ^o_{sol}\)
● the lattice energy of AlF₃, \(\Delta H ^o_{latt}\)
● the enthalpy changes of hydration of Al³⁺ and F⁻, \(\Delta H^o_{hyd}\). Include state symbols for all substances and ions.

(iii) Relevant data for this question are given.

Use these data and your energy cycle in (g)(ii) to calculate the \(\Delta H ^o_{latt}\) of \(AlF_3\).

▶️Answer/Explanation

Ans:

(a)(i) (number of possible) arrangements of particles / energy in a system
OR
measure / degree of disorder in / of a system [1]
(ii) positive / +
AND more gas molecules / particles in products
OR more moles / molecules in products / RHS [1]
(b) ΔH = (2 × 150) – (1 × 496) (= –196) [1]
OR
ΔH = (2 × 150) + (4 × 460) – (1 × 496) – (4 × 460) (= –196)
(c) ΔG = ΔH – TΔS seen or used with correct signs[1]
–238 = –196 – 298ΔS
ΔS = 42 / 298
ΔS = (+)0.141 / 0.1409 (kJ K⁻¹ mol⁻¹)
OR (+)141 / 140.9 (J K⁻¹ mol⁻¹) [1] ecf from ΔG = ΔH + TΔS
141 = (2 × 70) + S(O₂(g)) – (2 × 102)
S, O₂(g) = 205 / 204.94 (J K⁻¹ mol⁻¹)  [1] ecf

(d) iron(III) chloride / FeCl₃
AND same state / phase as reactants/H₂O₂ [1]
(e)(i) hydrogen peroxide / H₂O₂ AND +2.18 [1] 
(ii) ΔG =\( –nE^o_{cell}F\) [1]
ΔG = (–2 × 2.18 × 96500) = –420.7 (kJ mol⁻¹) [1] ecf
(f)(i) Nernst: (E =) \(E^o\) + (0.059 / z)log[ox] / [red] [1] u / c
OR (E =) \(E^o\) + (RT / zF)ln[ox] / [red]
OR (E =) 1.82 + (0.059 / 1)log(0.02 / 2)
E = 1.82 + (0.059 / 1)log(0.02 / 2) = (+)1.702 (V) [1] min 2sf
OR
E = 1.82 + [(8.314 × 298 / 1) × (96 500) ] ln(0.02 / 2) = (+)1.702
(ii) H₂O₂ + 2H⁺ + 2Co²⁺ → 2H₂O + 2Co³⁺ [1]
ECF for reverse equation from (f)(i) if E > 1.77 V
(g)(i) enthalpy change when one mole of gaseous ions
forms an aqueous solution / dissolves in water [1]

(iii) \(\Delta H_{latt} = –4690 + (3 \times – 506) – (–209) = –5999 (kJ mol^{–1})\)

Questions 4

(a) Topic – 28.1 General physical and chemical properties of the first row of transition elements, titanium to copper

(b)Topic – 28.1 General physical and chemical properties of the first row of transition elements, titanium to copper

(a) Cobalt(II) nitrate, Co(NO₃)₂, is a reddish-brown crystalline solid. It dissolves in water to form a solution containing [Co(H₂O)₆]²⁺ complex ions.
(i) Complete Table 4.1 giving the formula of the cobalt-containing species that is formed in each of the three reactions described.

(ii) Describe the colour change seen in reaction 3.
original colour of [Co(H₂O)₆]²⁺(aq) …………………………………………………………………………
final colour after addition of an excess of conc. HCl(aq) …………………………………………..
(b) Calcium nitrate, Ca(NO₃)₂, is a white crystalline solid. When heated, it starts to decompose at approximately 500°C.
(i) Write an equation for the decomposition of Ca(NO₃)₂.
(ii) Suggest temperatures at which Mg(NO₃)₂ and Ba(NO₃)₂ start to decompose. Explain your answer.
temperature at which Mg(NO₃)₂ starts to decompose …………………………………………. °C
temperature at which Ba(NO₃)₂ starts to decompose ……………………………………………°C
explanation ………………………………………………………………………………….

▶️Answer/Explanation

Ans:

(a)(i) • Co(OH)₂ OR Co(OH)₂(H₂O)₄
• \([Co(NH_3)_6]^{2+}\) OR \([Co(NH_3)_6]^{3+}\)
• [CoCl₄]²⁻
any two [1] all three [2]
(ii) pink to
blue [1]
(b)(i) 2Ca(NO₃) 2 → 2CaO + 4NO₂ + O₂
OR Ca(NO₃)₂ → CaO + 2NO₂ + ½O₂ [1]

(ii) M1: Mg(NO₃)₂ below 480 °C,
Ba(NO₃)₂ above 520 °C BOTH [1] u / c
M2: ionic radii of M2+ increases down the group
OR radii of Ba²⁺ is greater (than Mg²⁺)
OR charge density of M2+ decreases down the group
OR charge density of Ba2+ is smaller (than Mg2+) [1] ORA u / c
M3: (larger cations) polarise / distort anion / \(NO_3^–\) less
OR
(larger ions) weaken N-O / N=O (bond) less
[1] ORA

Questions 5

(a) Topic -28.1 General physical and chemical properties of the first row of transition elements, titanium to copper

(b)Topic – 13.3 Shapes of organic molecules; σ and π bonds

(c)Topic -27.1 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds

(d)Topic – 2.2 The mole and the Avogadro constant

Transition elements behave as catalysts and can form complex ions.
(a) Explain why transition elements behave as catalysts.

(b) Silver forms the linear complex ion \([Ag(CN)_2]^–\). Copper forms the tetrahedral complex ion \([Cu(CN)_4]^{3−}\). Titanium forms the complex [TiCl₄(diars)₂], where diars is a neutral bidentate ligand.
(i) State the oxidation state and the coordination number of titanium in [TiCl₄(diars)₂].
oxidation state …………………………
coordination number …………………………
(ii) Draw three-dimensional diagrams to show the shapes of [Ag(CN)₂]⁻ and [Cu(CN)₄]³⁻ in the boxes. Label one bond angle on each diagram.

(c) The numerical value of the stability constant, Kstab, of the copper(I) complex [Cu(CN)₄]³⁻ is \(2.0 × 10^{27}\).
(i) Write an expression for the \(K_{stab}\) of [Cu(CN)₄]³⁻.

(ii) In a solution the concentrations of CN⁻ and [Cu(CN)₄]³⁻ are both 0.0010 mol/dm³.  Use your expression from (c)(i) and the value of \(K_{stab}\) to calculate the concentration of \(Cu^+\)(aq) in this solution.

(d) A piece of a copper-containing alloy has a mass of 0.567g. It is dissolved in an acid giving 100.0 cm³ of a blue solution in which all the copper is present as Cu²⁺ ions. An excess of KI(aq) is added to a 25.0 cm³ sample of this solution. All of the copper is precipitated as white CuI(s). Cu²⁺ ions are the only component in the solution that react with KI(aq). This is reaction 1.
reaction 1 \(2Cu^{2+} + 4I^−\to  2CuI + I_2\)
The liberated I₂ is then titrated with 0.0200 moldm⁻³ S₂O₃²⁻.  This is reaction 2.
reaction \(2 I_2 + 2S_2O_3^{2–} \to 2I^− + S_4O_6^{2–}\)
The titration requires 20.10 cm³ of 0.0200 mol/dm³ S₂O₃²⁻ to reach the end-point.
(i) Calculate the number of moles of I₂ that are reduced in this titration.

(ii) Calculate the number of moles of copper in the original piece of alloy.

(iii) Calculate the percentage of copper in the alloy.

(iv) Suggest why a solution of Cu²⁺ is coloured but solid CuI is white.

▶️Answer/Explanation

Ans:

(a) more than one (stable) oxidation state [1]
empty / vacant (d) orbitals are energetically accessible
OR empty / vacant (d) orbitals can form dative bonds with ligands
[1]
(b)(i) oxid. no. = + 4 AND
coord. no. = 8 [1]

(c)(i) \(K_{stab} = [[Cu(CN)_4]^{3–}] / [Cu^+] [CN^–]^4\)
[1]
ALLOW use of [[Cu(H₂O)₆]+]
(ii) [Cu⁺] = 5.0 × 10⁻¹⁹ (mol dm⁻³) [1] min 1sf
ECF from reversed ratio 5(c)(i)
(d)(i) mol of I₂ = 0.5 × 0.02 × 20.1 / 1000 = 2.01 × 10⁻⁴
[1] min 2sf 
(ii) mol of Cu = 2.01 × 10⁻⁴ × 2 × 4 = 1.608 / 1.61 × 10⁻³
[1] ecf min 2sf 
(iii) % of Cu = 100 × (1.608 × 10⁻³ × 63.5) / 0.567 = 18.0 [1] ecf 
(iv) Cu²⁺ is d⁹/d shell / sub-shell / orbitals is / are not full
AND Cu⁺ is \(d^{10} / d\) shell / sub-shell / orbitals is / are full [1]
d-d* transitions / d electron promotion
not possible / possible (linked correctly) [1]

 

Questions 6

(a) Topic -28.2 General characteristic chemical properties of the first set of transition elements, titanium to copper 

(b)Topic – 13.4 Isomerism: structural isomerism and stereoisomerism

(a) Five ligands are listed in Table 6.1.

(i) Complete Table 6.1 using the words monodentate, bidentate and polydentate only. Each of these three words may be used once, more than once, or not at all.
(ii) The molecule H₂NCH₂CH₂NHCH₂CH₂NH₂ is a tridentate ligand. Suggest the meaning of tridentate ligand.
(iii) Suggest how H₂NCH₂CH₂NHCH₂CH₂NH₂ acts as a tridentate ligand.
(b) Nickel forms the octahedral complex \([Ni(en)_2(H_2O)_2]^{2+}\). This complex can exist in three isomeric forms, listed in Table 6.2. One of these forms is a trans isomer, the other forms are two different cis isomers.

(i) Complete Table 6.2 using the terms polar or non-polar. Each term may be used once, more than once, or not at all.
(ii) Describe the difference between cis isomer 1 and cis isomer 2.

▶️Answer/Explanation

Ans:

(a)(i) NH₃ = monodentate
\(EDTA^{4–}\) = polydentate / hexadentate
CN– = monodentate
C₂O₄²⁻ = bidentate
any two [1] all four [2]
(ii) (ligand that) donates 3 lone pairs to central metal atom / ion
OR
(ligand that) forms 3 dative bonds to central metal atom / ion [1]
(iii) ref to using the electrons / lone pair on (each) N  / amine group [1] 
(b)(i) trans = non-polar
cis isomer 1 = polar
cis isomer 2 = polar ALL [1]
(ii) optical isomers / non-superimposable mirror images [1]
ALLOW enantiomers / they rotate polarised light differently

Questions 7

(a) Topic -21.1 Organic synthesis 

(b)Topic – 21.1 Organic synthesis 

(c)Topic -21.1 Organic synthesis 

(d)Topic -21.1 Organic synthesis 

Sunset Yellow is an additive used for colouring foods. A synthetic route for making Sunset Yellow is shown. Molecules E and G each contain one \(–SO_3 ^–\) group. These groups are unchanged in the formation of Sunset Yellow.

(a) State the molecular formula of the Sunset Yellow anion.
(b) Deduce the structures of E, F and G and draw them in the boxes in Fig. 7.1.
(c) Suggest suitable reagents and conditions for step 1 and 2.
(d) Predict the number of peaks in the carbon-13 NMR spectrum of the Sunset Yellow anion.

▶️Answer/Explanation

Ans:

(a) \(C_{16}H_{10}N_2O_7S_2^{2–}\) OR \(C_{16}H_{10}N_2O_7S_2\) [1]

(c) M1 step 1: HNO₂ OR NaNO₂ + HCl [1]
M2 step 1: T ⩽ 10 °C [1]
M3 step 2: NaOH(aq) / alkaline conditions [1]

(d) 14 / fourteen [1]

Questions 8

(a) Topic -21.1 Organic synthesis 

(b)Topic – 21.1 Organic synthesis 

(c)Topic -21.1 Organic synthesis 

(d)Topic -21.1 Organic synthesis 

(e)Topic -21.1 Organic synthesis 

(f)Topic-21.1 Organic synthesis 

Capsaicin is found in chilli peppers.

You should assume the CH₃O group is unreactive in the reactions involved in this question.
(a) Name all the functional groups in capsaicin in addition to the CH₃O group.
(b) Complete the equation for the reaction of capsaicin with an excess of Br₂(aq) in the dark. Draw the structure of the organic product in the labelled box.

(c) Capsaicin is heated with an excess of hydrogen gas in the presence of platinum metal. The six-membered ring reacts in the same way as benzene under these conditions. Draw the structure of the organic product formed.

(d) When capsaicin is treated with reagent J under suitable conditions one of the products is methylpropanoic acid, CH₃CH(CH₃)COOH.
(i) Identify reagent J and any necessary conditions.

(ii) There are three different peaks in the proton (1H) NMR spectrum of CH₃CH(CH₃)COOH in CDCl₃.

(e) (i) Capsaicin is heated with an excess of hot aqueous NaOH

(ii) Name the two types of reaction occurring in (e)(i).
(f) Draw the structure of the organic product L formed when capsaicin is treated with \(LiAlH_4\) in dry ether.

▶️Answer/Explanation

Ans:

(a) phenol, amide AND alkene / C=C all three needed [1]

(d)(i) hot AND concentrated acidified AND MnO4–/ KMnO4 all [1]

(ii) hydrolysis AND neutralisation / acid-base[1]

Questions 9

(a) Topic -21.1 Organic synthesis

(b)Topic – 21.1 Organic synthesis

(c)Topic -21.1 Organic synthesis

(a) Benzoyl chloride, C₆H₅COCl, can be made from ethyl benzene in a two-step process. A reaction scheme is shown.

(i) Draw the intermediate organic compound M in the box. [1]
(ii) Suggest suitable reagents and conditions for step 1 and step 2.
step 1 …………………………………………………………………………………………………………………
step 2 …………………………………………………………………………………………………………………
(iii) Identify the type of reaction in step 1 and step 2.
step 1 …………………………………………………………………………………………………………………
step 2 …………………………………………………………………………………………………………………

(b) C₆H₅COCl reacts with phenol, C₆H₅OH, to give the ester phenyl benzoate, C₆H₅COOC₆H₅. An incomplete description of the mechanism of this reaction is shown in Fig. 9.1.

(i) Complete the mechanism in Fig. 9.1 and include:
● all relevant dipoles (δ+ and δ–) and full electric charges (+ and –) on the species in box one and in box two
● all relevant lone pairs on the species in box one and in box two
● all relevant curly arrows to show the movement of electron pairs in box one and in box two
● the formula of the second product in box three.
(ii) Name this mechanism.
(c) Benzoyl chloride, chlorobenzene and chloroethane differ in their rates of hydrolysis when each compound is added separately to water at 25°C. Suggest the relative ease of hydrolysis of these three compounds. Explain your answer.

▶️Answer/Explanation

Ans:

(ii) hot (alkaline) KMnO₄ / MnO₄–[1]
SOCl₂ OR PCl₅ OR PCl₃ + heat[1]
(iii) oxidation [1]
(nucleophilic) substitution

box one:
• 1 dipole on C=O
• 2 curly arrow from O of phenol to C of acyl chloride
• 3 curly arrow from bond of C=O to O of acyl chloride
box two:
• 4 curly arrow from O-H bond to what was O of phenol
• 5 curly arrow from C-Cl bond to what was Cl of acyl chloride
• 6 curly arrow from O to reform C=O
• 7 + charge on what was O of phenol
• 8 – charge on what was O of acyl chloride
• 9 curly arrow start close to LP for bullet 3 OR 6 (from LP on O)
box three:
• 10 HCl / \(H^+Cl^–\)
any two [1] any five [2] any eight [3] all ten [4]
(ii) (nucleophilic) addition-elimination [1]

(c) chlorobenzene, chloroethane, benzoyl chloride [1] u / c
explanation linked to their order
• correct link to: strengthening (ArCl / RCl) C-Cl bond
OR weakening (RCOCl) C-Cl bond
OR C-Cl bond has partially double bond character (ArCl)
OR C-Cl is more difficult to break (linked correctly)
chlorobenzene:
• lone pair / p-orbital on Cl overlaps / delocalised / incorporated with ring
benzoyl chloride:
• C of C-Cl has most electron deficient
OR has an electronegative oxygen atom
 / two electronegative atoms / electron withdrawing C=O group
chloroethane
• electron donating effect / positive inductive effect of alkyl / R group
any two [1] any three [2]

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